The voltage-gated potassium channel hERG (human ether-a-go-go-related gene) is the primary pore-forming subunit of the rapidly activating delayed rectifier potassium channel current (IKr) in the heart. The physiological role of cardiac IKr is th repolarization of the ventricular action potential. Although it is known that certain genetic mutations of hERG (or acquired conditions such as hypokalemia) can affect IKr, our understanding of the specific protein-protein interactions underlying hERG regulation are not well known. The cytoplasmic C- terminal portion of hERG was previously used to conduct a yeast two hybrid screen of a human cardiac library for proteins that might regulate ion channel localization, stability, and relative surface expression. This screen identified TRIOBP-1 (also known as Tara), an F-actin binding protein associated with cytoskeletal dynamics, as a putative hERG interacting protein. We hypothesize that TRIOBP-1 interacts with hERG to regulate ion channel surface expression, density, localization, and excitability. First, we will test the prediction that TRIOBP- 1 domains functionally associate with hERG protein to modulate hERG channel currents and surface expression using a combination of whole-cell patch clamp electrophysiology, Frster resonance energy transfer (FRET) measurements, and Western blotting in a HEK293 cell line as well as in hiPSC-CMs. Second, we will investigate a series of TRIOBP-1 point mutations previously associated with Long QT Syndrome Type II (LQT2) to explore their modulatory effects on hERG channel properties in HEK293 cells. Together these experiments provide a potential therapeutic target for hERG channel-related LQT2 and provide insight into hERG channel regulation and the proteins with which it interacts.